Protective helmet



FIG. 1 is a front perspective view of a protective helmet showing my new design;

FIG. 2 is a rear elevational view thereof;

FIG. 3 is a front elevational view thereof;

FIG. 4 is a top plan view thereof; and,

FIG. 5 is a side elevational view thereof. 

The ornamental design for a protective helmet, as shown and described. 